Commentary: Taking stock and moving forward - the need to consider the influence of loss to follow-up in autism screening research.

This commentary highlights the limitations of many existing population-based studies examining the utility of the Modified Checklist for Autism in Toddlers, Revised/Follow-Up (M-CHAT-R/F) in screening for autism. We expound on three major factors: (a) the limited number of screen-negative children who undergo diagnostic evaluations, (b) the substantial number of children who screen positive and were subsequently lost to follow-up (i.e. without further diagnostic evaluations), and (c) the sizeable number of children who did not complete the full two-stage screening process as intended. Each of these factors can lead to erroneous estimates of the psychometric properties, specifically, the sensitivity, specificity, and negative predictive value. Hence, we emphasize the need for future studies to increase the number of children who screen negative and receive a diagnostic evaluation and ensure that these children are selected at random without a higher likelihood for the presence of autism. It is also imperative that concrete steps are taken to minimize the number of screen-positive children who are lost to follow-up both within and after the screening process. Both of these will play a major role in ensuring more robust results from empirical research that can guide the clinical implementation of the M-CHAT-R/F.